01643726

Monograph

http://www.trb.org/Main/Blurbs/176360.aspx

This research sought to develop a rapid screening nondestructive test procedure utilizing stress wave interrogation for detection of fatigue cracks in steel anchor rods. The method would be able to detect the presence of a fatigue crack with greater reliability than visual inspection. The proposed method is similar to the impulse response method used for integrity testing of concrete piles. In this research, an analogy is drawn between a steel anchor rod partially embedded in a concrete foundation and a concrete pile partially embedded in soil. The anchor rod assembly represents a much smaller length scale with a higher degree of geometric complexity (anchorage hardware including nuts, washers, baseplate, anchor plate) as compared to a concrete pile. The additional geometric complexities of anchorage systems complicate signal processing and data interpretation. This requires additional signal interpretation methods. A full-scale structure-foundation anchorage assembly was constructed for an experimental evaluation of the proposed method for fatigue crack detection. To perform a test, an accelerometer was coupled to the top surface of an anchor rod, and the surface was struck with an instrumented hammer. In order to identify indicators of fatigue cracking, several damage-sensitive features extracted from univariate and multivariate regression models were evaluated. Of the investigated features, alpha-based regression coefficient was found to be the most reliable indicator of anchor rod cracking. Evaluation of impulse response data for the purpose of damage identification involves measuring the variation in the response signal from a known baseline. Since the recorded data is a collection of discrete points, regression models are employed to develop best-fit functions for statistical comparison. Autoregressive models models were used to fit accelerometer recordings normalized by the applied impulse. It was found that by establishing a baseline measurement for an uncracked rod, and evaluating the change in Mahalanobis distance between the alpha coefficients of regression models fitting the test data, the test method was able to identify artificial cracks at the base of the leveling nut (a region known to be susceptible to fatigue cracking), extending 1/4 and 1/2 of the rod diameter in depth, with at least 95% confidence.

This NCHRP-IDEA investigation was conducted by Lehigh University.

NCHRP Idea Project 175

English

47p

2017-6

Final Report

Digital/other

Appendices; Figures; Photos; References; Tables

Anchor bolts; Fatigue cracking; Nondestructive tests; Stresses; Test procedures

Impulse response

Innovations Deserving Exploratory Analysis (IDEA) (Program)

Highways; Materials

TRIS, TRB, ATRI

Aug 17 2017 10:28AM